1. Field of the Invention
The present invention relates generally to the control of an internal combustion engine having an air introduction device in the engine exhaust.
2. Background of the Invention
Vehicle engines have used a secondary air pump in the engine exhaust to introduce air to increase emission control. The pumps are attached, for example, to the exhaust manifold of the engine and pump ambient air into the exhaust. The secondary air can reach with rich exhaust gasses to rapidly heat the catalytic converter. Further, schemes have been developed for estimating the airflow introduced via the secondary air pumps. An example of such a system is described in U.S. Pat. No. 6,044,643.
The inventors herein have recognized a disadvantage with the above approach. In particular, as vehicle conditions change and components age, accuracy of open loop estimates can vary. Degradation in the estimate of airflow introduced via a secondary air pump can have result in degraded emission control. This is especially true in a system that attempts to exothermically react rich exhaust gasses with secondary air. In other words, if the estimate of airflow is inaccurate, the overall mixture may provide incomplete exothermic reaction, resulting in degraded emissions.